The invention relates to a system for measuring a change in position of a medical device, such as an endoscopy capsule, and to an appliance which utilizes this measurement in order to influence the position of the medical device.
Endoscopy capsules are used increasingly in medicine to diagnose or treat the inside of a patient. An endoscopy capsule can contain inter alia medical instruments for instance for biopsy or for introducing medicines into the body and/or image systems such as cameras. Furthermore, a permanent magnet can be integrated in the capsule, which affords the capsule a magnetic dipole moment, so that that it can be maneuvered at will with the aid of a magnetic coil arrangement as described in DE 103 40 925 B3 for instance.
With examinations inside the body using a medical device such as an endoscopy capsule, the position of the device is generally monitored and if necessary influenced. For instance, with an examination of the stomach, this is half filled with water and the endoscopy capsules floats on the water surface. When recording images of the inside of the stomach, the problem arises that the capsule and with it the camera are moved as a result of the water movement which cannot be avoided, so that only unclear, blurred images can be recorded. In the event that a series of images of a certain region is to be recorded, it is necessary for the capsule to be stationary.
For position determination purposes, electromagnetic measuring methods mostly use low-frequency magnetic alternating fields, which penetrate the human body in an almost uninfluenced fashion, thereby rendering an absolute position determination possible. A system of this type is described in WO 2005/120345 A2. Nevertheless, known systems on the one hand are disadvantageous in terms of a limited measuring accuracy. On the other hand, as a result of a poor signal-to-noise ratio and the necessary long integration time associated therewith, the temporal resolution is relatively minimal and the measuring value delay is comparatively great. Alternatively, phase difference measurements on high-frequency electromagnetic waves were proposed for the absolute position measurement of medical devices in the inside of the body. Account was not taken here of the fact that the wave propagation through body tissue with a different dielectric constant and conductivity results in a considerable deformation of the spherical wave front in the free space. Nevertheless, to enable an absolute position determination, complex correction methods are needed.